It has long been desirable, and in many cases necessary, to somewhat apply a metal laminate, usually precious metal, to a strip of a different metallic material. For example, in the electronic industry, gold-plated components, such as semi-conductors, connectors, etc., are frequently used in order to impact certain desirable characteristics, such as electrical conductivity, corrosion resistance, etc., to the metal strip. Obviously, it is not economically feasible to make such components completely of gold, and hence the procedure has been to use a less expensive metal, to which the gold or other previous metal is applied.
There are numerous techniques by which a previous-metal laminate can be applied to a metallic strip. For example, the laminate can be applied by simply cladding the different metals together, by means of a conventional cold-rolled bonding process, or by the equally conventional technique of soldering and then rerolling. In addition, a precious-metal laminate can be applied by putting a layer of the metal in molten form on the base metallic strip. Perhaps the most desirable technique, however, and the technique with which the instant invention is concerned, is electroplating; this technique being particularly desirable, since the thickness of the plating can be effectively controlled, desired hardness and wear resistance can be obtained using only minor amounts of other metals, etc.
Although electroplating techniques are well known in the art, most are usable only where the entire base strip is to be plated on one or both sides. Where, however, a base metal strip is being plated with a previous metal, such as gold, for electronic uses, it is usually necessary that only one side of the strip be plated, and it is further normally necessary that the plating cover only a portion of one side of the strip. Expressed differently, in many cases the functional requirements are such as to be met by plating a relatively thin continuous stripe of precious metal onto one surface of the base metal strip. The present invention is directed to apparatus for continuously plating such a stripe on one side of a metal strip.
The basic concept employed in the present invention embodies use of a rotatably mounted, hollow plating wheel having a slot extending around the peripheral circumference of the wheel, said slot communicating with the interior of the wheel. Means are provided for maintaining the metal strip to be plated in driving engagement with at least a portion of the periphery of said wheel, said strip being wider than the width of the aforesaid slot and covering same, whereby a portion of the inner surface of the strip will be exposed to the interior of said wheel. Distribution means are provided within the wheel for directing a flow of electrolyte which is fed to the wheel against the exposed inner surface of the strip to effect plating of said exposed inner surface, it being understood that suitable anode means are associated with the wheel, and the metal strip is connected as a cathode in order to complete the electrolytic circuit.
The above concept, to the extent that it is described in the paragraph supra, is not novel, it being noted that a similar system is disclosed and described in Meuldijk et al. U.S. Pat. No. 3,819,502 dated June 25, 1974, which patent represents the closest prior art of which applicant is aware.
Although the wheel plating technique disclosed and described in the above-noted Meuldijk patent is reasonably effective, it does possess certain inherent disadvantages. Reference is made to the fact that in Meuldijk plating takes place through a substantially stationary pool of electrolyte liquid, thus reducing agitation and hence the rate at which plating takes place. In addition, in Meuldijk the electrolyte is introduced to the plating wheel by gravity, since a relatively small volume of electrolyte is continuously being exchanged, thus limiting the rate of introduction of electrolyte to the apparatus. This also lessens the rate at which the strip can be plated in Meuldijk.
The present invention, while utilizing the same basic wheel system as in Meuldijk, overcomes the above-discussed disadvantages of the latter, whereby a much higher plating rate can be effectively obtained. More specifically, in the present invention, fixed, monorotatable distribution means are mounted within the plating wheel, said distribution means defining separate electrolysis and suction chambers. Means are provided for continuously pumping electrolyte at a relatively high rate (higher than gravity) to the electrolysis chamber which directs the electrolyte against the exposed inner surface of the strip to effect electroplating of same in the same general manner as in Meuldijk. In addition, means are provided for applying a negative pressure to the suction chamber whereby excess electrolyte is immediately drawn off from the electrolysis chamber to the suction chamber from which it is evacuated to a reservoir for subsequent recirculation to the electrolysis chamber. The suction chamber is specifically designed so as to have no anode whereby no appreciable plating of the strip takes place at that location, but rather plating takes place only at the location of the electrolysis chamber. Since, however, excess electrolyte is immediately drawn away from the electrolysis chamber, plating never takes place through a standing pool of liquid, thus permitting more rapid plating. Preferably, the suction chamber is located generally at a 5 to 7 o'clock position; while a pair of oppositely disposed electrolysis chambers are generally located at 2 to 5 o'clock and 7 to 10 o'clock positions. By having the suction chamber so located between the electrolysis chambers, flow of electrolyte from the latter to the former is enhanced by gravity. Thus, the only place where a standing pool of liquid may exist at any time in the present apparatus is in the suction chamber; but since by specific design little or no plating is taking place at said location, the presence of such a standing pool does not affect the rate of plating. Also, since the suction chamber in the present apparatus rapidly exhausts relatively large amounts of electrolyte, a greater rate of exchange of electrolyte to and from the apparatus is permitted; whereby instead of using gravity feed for the electrolyte, the latter may be introduced at a higher rate by pump means, all of which further enhances the rate of plating achieved by this invention.
A further feature of the present invention is the provision of means for achieving a more effective line contact between the inner surface of the strip and the opposite edges of the peripheral slot whereby more effective engagement of the strip and the edges of the slot is achieved, this being important not only to obtain good definition of opposite sides of the plated stripe, but also to insure a proper seal, which is necessary to maintain the desired negative pressure in the suction chamber.
Still another feature of the present invention is the provision of a novel belt system for engaging and supporting the outer surface of the metal strip to be plated, said system being preferably used in those situations where auxiliary means are necessary to insure proper driving contact of the strip to be plated with the plating wheel, such as where the strip is too thin to carry the required back tension, or where the strip is too thick to conform properly against the circumference of the wheel.
Other objects, features and advantages of the invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.